There are a range of technologies available that allow fluid pressure to be used to pump other fluids. These devices are, in essence, pressure exchange devices, and can also be used to extract pressure from fluids.
The Seimag 3 chamber pipe, DWEER and ERI systems (discussed in further detail below) are fluid pressure exchange systems in which the fluids can interact (i.e. to mix) to some extent.
There is a broad family of other fluid pressure exchange devices that have a membrane (flexible hose) inside a rigid pipe to define an annulus (between the hose and the pipe) and a volume (within the hose). The annulus and volume can be used to exchange or recover energy between two fluids and at the same time keeping the fluids separated to prevent mixing and improve energy transfer efficiency. Energy transfer in these pumps is typically through a positive displacement action.
Examples of such pumps are described in the following patent applications and patents: PCT/AU2003/000953 (West and Morriss), GB 2,195,149A (SB Services), WO 82/01738 (Riha), U.S. Pat. No. 6,345,962 (Sutter), JP 11-117872 (Iwaki), U.S. Pat. No. 4,543,044 (Simmons), U.S. Pat. No. 4,257,751 (Kofahl), U.S. Pat. No. 4,886,432 (Kimberlin), GB 992,326 (Esso), U.S. Pat. No. 5,897,530 (Jackson).
Of these, the pump described in PCT/AU2003/000953 (West and Morriss) has achieved commercial application in the mining industry. In its typical use, a dirty or corrosive fluid is pumped inside the flexible hose, under low pressure, and another fluid such as hydraulic oil is pumped into the annulus at high pressure—causing the dirty or corrosive fluid to exit the hose under high pressure. The use of hydraulic oil as the energy source, allows the energy to be efficiently developed in a clean, long life environment.
Some other typical applications using energy exchange devices are as follows.
(i) Hydraulic Hoisting
Hydraulic hoisting is the principle of pumping a slurried mineral ore (or similar) from a depth within a mine, either to the surface or a higher level in the mine. The mine may be either open cut or underground. Typical alternative methods of removing ore from mines are by hoisting in a skip, by conveyor, or by dump truck. Hydraulic hoisting should in principle provide a lower life cycle cost than these alternatives—but is yet to establish a significant position in the market place.
Existing forms of hydraulic hoisting generally consist of;    1. Using a piston diaphragm or other high pressure pump to pump a homogeneous slurried ore to the surface of a mine. In this case, the slurry is pumped to the surface, and nothing is returned or recirculated back to the original pumping point, and hence no pressure recovery is possible; or    2. Using a three chamber pipe system (eg. Siemag type system) to pump a slurried ore to the surface of a mine, but using recirculated water from the surface to assist in pumping the slurry. The 3-chamber system relies on sequentially filling and discharging 3 chambers with slurry and then water.
Within this system, one chamber is initially filled with slurry, before discharging it under high pressure with water. During the discharge stroke, another chamber is filled with slurry, then discharged by the high pressure water, while the third chamber is being filled. The process then continues with this third chamber discharging and the first chamber filling, in an on-going sequence.
Although this system recovers energy from the recirculated water, mixing can occur between the two mediums, which also results in energy losses and dilution or contamination of the slurry. Also, it is usually necessary to apply additional energy to the system to hoist the slurry from the mine due to the density differences between the water and the slurry and due to friction losses in the system.
Some hydraulic hoisting systems have been proposed where a dense slurry media is used as the carrier for pumping the ore to be removed from the mine (in a particulate form), and pressure is recovered from the dense media as it is recirculated back into the mine. (eg via a 3-chamber pipe system) (see: Hydraulic Hoisting for Platinum Mines, 2004, Robert Cooke et al).
As noted, in many of the pressure recovery circuits, make-up flow and or pressure must be applied to the circuit to maintain pressure and flow balances.
(ii) Integrated Cooling and Dewatering Systems
In these integrated systems, water is typically cooled on the surface of the mine, then pumped underground. As a result of which, it develops considerable (potential) energy. This energy is recovered in three chamber pipe systems or Pelton wheel type systems and used to help pump dirty water from the mine.
(iii) Reverse Osmosis
In sea water reverse osmosis systems, the salty sea water is usually brought up to around 7,000 kPa (1000 psi) through multi-stage centrifugal pumps. The pressurised water is then fed into reverse osmosis membrane chambers, from which clean water exits on one side of the membrane, and a high salt concentration water exits from the other side. The high salt concentration water is still at high pressure, but approximately half the flow rate of the sea water inflow.
Various pressure recovery systems exist to recover the energy from the high salt concentration water, (eg. DWEER (solid floating piston in pipe) and ERI (rotating liquid piston systems)). These either allow some level of mixing to occur between the two mediums, or have the potential for friction (between the solid piston and walls) which together result in energy and efficiency losses. Also the use of multi-stage pumping as the primary pumping mechanism is not the most efficient technology available at these pressures.